1. Technical Field
The present invention relates to a liquid crystal dropping device which comprises a syringe for storing liquid crystal material, a plunger which is reciprocated in the syringe and a driving unit for driving the plunger, to drop liquid crystal material onto a substrate included in a liquid crystal display apparatus, and to a method of manufacturing a liquid crystal display apparatus.
2. Description of Related art
Among display apparatuses, a liquid crystal display apparatus has characteristics of being thin and consuming a small amount of electricity. Specifically, a liquid crystal display apparatus comprising a TFT substrate having a switching element such as a thin film transistor (TFT) or the like for each pixel presents high performance including high contrast ratio and good response characteristics, and is thus preferably used for a television receiver, a personal computer and so forth.
The display panel of a liquid crystal display apparatus has a pair of substrates (TFT substrate and color filter substrate) constituted by transparent glasses facing each other with a predetermined distance in between and a liquid crystal layer interposed between these substrates. The pair of substrates are bonded to each other with a seal material interposed in between, including a liquid crystal layer between the substrates.
Examples of the method of filling a space between the substrates of the display panel with liquid crystal material include dipping, dispensing and so forth. Such a method includes bonding a mother glass substrate of the TFT substrate to a mother glass substrate of the color filter substrate through a seal material, filling, for each divided panel, liquid crystal material through an opening of a seal pattern, and thereafter sealing the opening, to obtain a display panel.
In recent years, One Drop Filling (ODF) is often employed as a method of filling the inside of the display panel with a liquid crystal material.
The ODF is a method of dropping liquid crystal material into a frame of a seal pattern of the mother glass substrate of one of the substrates (TFT substrate or color filter substrate) before being aligned with the other substrate, without an opening in the seal pattern, and thereafter aligning and bonding the substrate with the other one of the substrates under reduced pressure. The ODF has an advantage of tremendously reducing the cycle time for liquid crystal material.
The liquid crystal dropping device used in the ODF method includes a syringe for injecting liquid crystal material, a plunger which is reciprocated in the syringe and a driving unit for driving the plunger, and is configured to switch the syringe and the plunger in accordance with a substrate and to drop liquid crystal material onto the one of the substrates.
In the ODF method, a syringe is filled with liquid crystal material which is then dropped onto the substrate, possibly causing the liquid crystal material to have foreign substances mixed therein compared to the dipping method.
As the plunger is stopped after switching the syringe and the plunger in accordance with the substrate until the liquid crystal material is started to be dropped onto the next substrate, the leading end of the plunger made of synthetic resin is in contact with the inner wall of the syringe and thus the leading end may be adhered to the inner wall. If the plunger is operated for dropping liquid crystal material in such a state, the adhered synthetic resin may be peeled because of the high resistance between the leading end and the inner wall of the syringe, so that dust generated by peeled resin may get mixed into the display panel as foreign substances.
When foreign substances get mixed into the display panel, problems arise in that, for example, a display failure such as a failure of visually recognizing bright dots (luminous-dot failure) is caused, thereby degrading the display quality and lowering the yield.
To address such problems, Japanese Patent Application Laid-Open Publication No. 2006-133251 discloses an invention of a liquid crystal dropping device comprising a filtering unit such as a filter in the transfer path of liquid crystal material between a container for storing liquid crystal material and a nozzle for dropping the liquid crystal material onto a substrate.
FIG. 7 is a schematic side view illustrating the structure of a liquid crystal dropping device 71.
The liquid crystal dropping device 71 includes a liquid crystal bottle 2, a three-way valve 3, a liquid crystal ejecting part 4, a nozzle 5 and a driving unit 7. Liquid crystal material 61 is stored in the liquid crystal bottle 2. The lower end of the liquid crystal bottle 2 is connected to one end of a flow pipe 24, while the other end of the flow pipe 24 is connected to the three-way valve 3. One end of the flow pipe 25 is connected to the three-way valve 3, while the other end of the flow pipe 25 is connected to the liquid crystal ejecting part 4.
The liquid crystal ejecting part 4 includes a syringe 41 and a plunger 44 located in the syringe 41. The plunger 44 includes a slide part 42 which has substantially the same diameter as the inner diameter of the syringe 41 and slides in the syringe 41, and a support 43 which has a rod-like shape and supports the slide part 42. The driving unit 7 is constituted by, for example, a stepping motor which controls the extruded amount of the slide part 42 by the amount of rotation. One end of the flow pipe 51 is connected to the three-way valve 3, while the other end thereof is connected to the nozzle 5. A filter 28 is provided at a midway part of the flow pipe 51.
In the case where the liquid crystal material 61 is dropped onto a substrate, the flow pipe 24 side and the flow pipe 25 side of the three-way valve 3 are opened, and the plunger 44 is lowered to feed a predetermined amount of liquid crystal material to the syringe 41. Next, the flow pipe 25 side and the flow pipe 51 side of the three-way valve 3 are opened, and the plunger 44 is raised by the driving unit 7 to feed liquid crystal material to the nozzle 5, from which the liquid crystal material is dropped onto the substrate.
As the liquid crystal dropping device 71 includes the filter 28, foreign substances which may be mixed into the liquid crystal material 61 are removed, thereby suppressing the occurrence of a display failure such as a luminous-dot failure and suppressing the degrading in the display quality and lowering in the yield.